1. Inverters
Inverters take dc from a
battery (etc) and
convert it electronically
to ac power.
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3. Block diagram of and inverter
AC Out
DC In Switches Transformer Rectifier Filter DC Out
DC to AC
Output is sampled to
adjust switching for
voltage regulation
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4. Inverter OPERATION
• Inverters are classified by their ac output
waveform.
– Square wave
– Modified sine wave
– True sine wave
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5. Inverter operation
Sine Wave
Square Wave
Modified Square Wave
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6. Inverter operation
• Most smaller inverters are either square wave
(cheap) or modified square wave.
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7. Inverter operation
By closing and opening the switch rapidly, a square wave supply to
the transformer is achieved. This used to be done mechanically with
a “vibrator”. (Yeah! I know…)
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8. Inverter operation
The switches close in turn, producing a pseudo-AC in the primary.
Not that rectification is centre-tapped, full wave, with an L filter.
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9. Inverter operation
Here the rectifier is a full wave, bridge, with L filter.
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10. Inverter operation
A single winding is used here on the primary, with the switches
closing is sequence to provide AC to the primary.
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11. Vibrator
Vibrator
Here is what one looks like.
Inside are vibrating mechanical
contact points that oscillate and
generate a low voltage AC
signal from the DC voltage
applied to it from the battery.
The AC signal then feeds a
transformer where the voltage
is increased.
AC Out
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13. Square waves
• Cheap
• Very poor regulation
• Produce large amounts of RFI
• Very rough AC
• Large amounts of harmonics
• Often used for small appliances eg; fluro lights
Very few but the very cheapest inverters any more are square
wave. A square wave inverter will run simple things like tools
with universal motors with no problem - but not much else.
These are seldom seen any more except in small, very cheap
or very old inverters.
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